The present invention is related generally to control circuits for RF signal power amplifiers, and more particularly to improved, temperature compensated, automatic output control circuitry for RF signal power amplifiers.
Prior art power amplifiers typically only have one output power level. Such power amplifiers were adjusted during manufacture to the desired output power level. In some applications, it was desirable to have two power settings, a low and a high setting. The RF signal power amplifier for such applications would have one setting for the high power level and another for the low power level.
More recently, it has become advantageous to reuse radio channels in some radio communications systems. Therefore, in order to avoid interference between two RF signal power amplifiers using the same frequency, it is desirable to have many different selectable output power levels. For example, four different power levels are provided for in the RF signal power amplifier in the mobile radiotelephone described in Motorola Instruction Manual No. 68P81039E25, entitled "Advanced Mobile Phone System", and published by Motorola Service Publications, 1301 E. Algonquin Road, Schaumburg, IL, 1979. The four power levels are produced by varying reference voltage which is applied to automatic output control circuitry. However, such automatic output control circuitry cannot accurately maintain a wide range of power settings in RF signal power amplifiers operable at several different RF signal frequencies and subjected to a wide range of temperatures.